HomeMy WebLinkAbout211404 - SANITARY SEWER DEMAND CALCS (Signed) 2022.09.08 SANITARY SEWER
DEMAND CALCULATIONS
LOT 2
MINOR SUBDIVISION NO. 437
Prepared for:
VISSER ARCHITECTS, P.C.
163 QUIET WATER WAY
Manhattan, MT 59741
Prepared by:
*IMEG
Engineering and Surveying Inc.
Project Number: 211404
September 2022
INTRODUCTION
The Evergreen Shops Site Plan project proposes to develop Lot 2,Minor Subdivision No.437 into
a commercial shop building consisting of three units. The property is located within the City of
Bozeman and is zoned as M-2 (manufacturing and industrial district). The property is fronted by
a city street, with Evergreen Drive being adjacent to the west property boundary. Water and
sanitary sewer mains are located within Evergreen Drive to which a single water and sanitary
sewer service will connect to the proposed building as shown on civil sheet C3.0. No fire lines
are proposed.
Sanitary Sewer Design Load
The flow rates used herein are according to the City of Bozeman Design Standards and
Specifications Policy (DSSP) dated March 2004 with approved Addendum No. 7 approved March
13, 2020. Based on Table V-1, the sewer discharge rate for a manufacturing and industrial use
property (M-2) is 960 gallons/acre/day. As such, this 1.040-acre lot would result in a sanitary
sewer discharge rate of 998.40 gallons per day.The peaking factor for the design area is determined
by figuring the equivalent and inserting the population into the Harmon Formula. An estimated
total of 32 employees and customers is assumed.
Harmon Formula: Peaking Factor= (18 +Po s)/(4 +Po.$)
where: P =Population in thousands
Peaking Factor= (18 + 0.0160-5)/(4 + 0.0160.$)
Peaking Factor=4.39
Assumed infiltration rate = 150 gallons/acre/day= 150 (1.040 acres) = 156 gal/day
The peak flow rate is calculated by multiplying the City's design generation rate by the peaking
factor, and adding the infiltration rate:
Peak Flow Rate = (998) (4.39) + 156 gpd = 4,542 gpd
= 3.15 gpm
= 0.007 cfs
The capacity of a 4-inch service is checked using Manning's Equation:
Qf,u = (1.486/0.013)AR2i3Sv2
For an 4-inch service:
Manning's n = 0.013 for PVC Pipe
Minimum Slope = 0.02 ft/ft
A=area= (3.14/4)d 2= (3.14/4)(4/12)2= 0.0873 ft2
P =perimeter=2(3.14)r=2(3.14)(2/12) = 1.0472 ft
R=hydraulic radius =A/P = 0.0872/1.046 = 0.0834 ft
R2i3 = 0.1908 ft
S = 0.02 ft/ft
Sia = 0.1414ft/ft
Qf,n = (1.486/0.013)(0.0873)(0.1908)(0.1414) = 0.2692 cfs
Q75%= 0.75*Qf ii = 0.75*0.2692 cfs = 0.2019 cfs
Connection:
Q/Qf„u = 0.007/0.2692 =0.026 or 2.6%
Based on these calculations, a 4-inch sewer line has adequate capacity to carry the design flows
for the project. The City of Bozeman will confirm that their wastewater system has the capacity to
handle this peak flow downgradient of the project.